Microcomputers normally provide a single expansion slot or other connection point for external disk drives. Controller cards designed for attachment to the interface had previously provided control capability for two "dumb" disk drives. The host computer accesses either of the drives through the controller by the use of a common address selecting the controller and a disk drive selection bit provided to a command register within the controller. The controller provides the status of both disk drives to the computer and interprets computer selection commands to activate one or the other drive as the selected drive.
More recently, intelligent or integrated disk drives have become available. The intelligent disk drive incorporates the controller within the disk drive unit, requiring only an address and data cable hook-up to the host microcomputer. In this configuration, however, one intelligent disk drive consumes the single expander port or connection point with the address and host data cables. Techniques have been developed for driving two intelligent disk drives from a common cable set; however, external jumper connections for designation of single or multiple disk operation, master or slave designation, and drive number designation have been required.
Operation of the intelligent disk drive, therefore, required selection of its configuration and installation of the appropriate jumper connections. As an example, if a disk drive were to be the master drive, or drive 0, in a two-drive hook-up, the jumper designating master drive would be installed. The jumper designating no second drive would not be installed, and the third jumper indicating a second drive present would be installed. Conversely, on the second drive, the first two jumpers would not be installed, and the third jumper designating a slave drive present would be installed. It should be noted that the master drive would not function properly if the slave drive were not present. For a master drive operating singly, the first and second jumpers would be installed, while the third jumper would not. The prior art technique described, therefore, required three jumpers uniquely installed for any configuration operation, singly or multiply. The present invention eliminates the requirements for multiple jumpers. A single jumper designating device address is sufficient.